Hypoxia inducible factor 1α gene (HIF-1α) splice variants: potential prognostic biomarkers in breast cancer

Background: Hypoxia-inducible factor 1 (HIF-1) is a master transcriptional regulator of genes regulating oxygen homeostasis. The HIF-1 protein is composed of two HIF-1 alpha and HIF-1 beta/aryl hydrocarbon receptor nuclear translocator (ARNT) subunits. The prognostic relevance of HIF-1 alpha protein overexpression has been shown in breast cancer. The impact of HIF-1 alpha alternative splice variant expression on breast cancer prognosis in terms of metastasis risk is not well known. Methods: Using real-time quantitative reverse transcription PCR assays, we measured mRNA concentrations of total HIF-1 alpha and 4 variants in breast tissue specimens in a series of 29 normal tissues or benign lesions (normal/benign) and 53 primary carcinomas. In breast cancers HIF-1 alpha splice variant levels were compared to clinicopathological parameters including tumour microvessel density and metastasis-free survival. Results: HIF-1 alpha isoforms containing a three base pairs TAG insertion between exon 1 and exon 2 (designated HIF-1 alpha(TAG)) and HIF-1 alpha(736) mRNAs were found expressed at higher levels in oestrogen receptor (OR)-negative carcinomas compared to normal/benign tissues (P = 0.009 and P = 0.004 respectively). In breast carcinoma specimens, lymph node status was significantly associated with HIF-1 alpha(TAG) mRNA levels (P = 0.037). Significant statistical association was found between tumour grade and HIF-1 alpha(TAG) (P = 0.048), and total HIF-1 alpha (P = 0.048) mRNA levels. HIF-1 alpha(TAG) mRNA levels were also inversely correlated with both oestrogen and progesterone receptor status (P = 0.005 and P = 0.033 respectively). Univariate analysis showed that high HIF-1 alpha(TAG) mRNA levels correlated with shortened metastasis free survival (P = 0.01). Conclusions: Our results show for the first time that mRNA expression of a HIF-1 alpha(TAG) splice variant reflects a stage of breast cancer progression and is associated with a worse prognosis. See commentary: http://www.biomedcentral.com/1741-7015/8/45